1. Field of the Invention
This invention relates to a connecting rod, and more particularly to a connecting rod of a fiber reinforced plastic material.
2. Description of the Prior Art
The connecting rods which have so far been employed are constructed as disclosed in the Japanese Laid-open Publication Nos. 56-155122 and 56-157420 of Japanese Utility Model Applications, such that the body of connecting rod has a bearing hole for a piston pin of a small diameter formed at one end thereof into which is inserted the piston pin and, at the other end thereof, is provided with a semi-circular recess forming a half part of a bearing hole for a crankshaft of a larger diameter connected to the crankshaft and with a block having a semi-circular recess corresponding to said recess and fixedly secured to the other end of the body by tightening up a pair of bolts thereby defining a crankshaft bearing hole. The purpose of this is to allow a back pressure to be exerted on the crankshaft bearing hole in the longitudinal direction of the rod member.
Accordingly, it is necessary to form longitudinally extending holes in the connecting rod body on both sides of the recess thereof and on both sides of the block (that is; in the critical part of the connecting rod). Therefore, in the case where the connecting rod is formed by a fiber reinforced plastic material, the fiber itself is interrupted or cut off by the bolt insertion holes to thereby reduce the effective sectional area of the critical part of the connecting rod and both ends of the fiber in the vicinity of the bolt insertion holes are cut off. Consequently, the load caused by tightening up the bolts and that due to the inertia force exerted in the crankshaft bearing hole portion will be borne by the shearing strength of the carbon fiber reinforced plastic material in the periphery of the recess on the side of the crankshaft bearing hole and also in the periphery of the recess on the side of the block. Therefore, there is a risk that the fiber reinforced plastic material cannot endure the loads caused on the crankshaft bearing hole portion with the result that the connecting rod is damaged or broken.